Obsessive-compulsive disorder is a heterogeneous cluster of syndromes that share aspects of both anxiety and affective disorders. Obsessive-compulsive disorder is epidemiologically and phenomenologically distinct from the compulsive character. Although both genetic and neuropsychological data suggest some biologic basis to obsessive-compulsive disorder, there is still insufficient information in both of these areas. Treatment with clomipramine, a tricyclic antidepressant, has proved useful for obsessional patients either as an adjunct to behavior therapy or as a primary treatment for patients who are not amenable to behavioral interventions.